Apparatus for coating continuously moving strip material with powders



APPARATUS FOR COATING GONTINUOUSLY MOVING Feb. 11, 1969 K. T. LAWSON ET AL 3,426,730

- STRIP MATERIAL WITH POWDER Filed Sept. 22, 1965 Sheet of 2 Feb. 11. 1969 K. T. LAWSON ET 3,426,730

APPARATUS FOR COATING CONTINUOUSLY MOVING STRIP MATERIAL WITH POWDER Filed Sept. 22, 1965 Sheet z of 2 United States Patent 3,426,730 APPARATUS FOR COATING CONTINUOUSLY MOVING STRIP MATERIAL WITH POWDER Kenneth Thomas Lawson, Marton, and Keith Judge Ascough, Levensdale, England, assignors to Head, Wrightson and Company, Limited, Thornaby-on- Tees, England, a United Kingdom corporation Filed Sept. 22, 1965, Ser. No. 489,132 Claims priority, application Great Britain, Sept. 28, 1964,

39,393/64 US. Cl. 118-636 Claims Int. Cl. B05!) 5/04 ABSTRACT OF THE DISCLOSURE This invention relates to apparatus for coating metal strip with powder.

It is already known to apply a coating of metal powder, such as aluminium powder, to a steel strip by spraying using for example a spray gun of well known construction.

It is also known to pass the metal powder through a high voltage field which has the effect of electrostatically charging the particles of the powder with a view to improving adhesion between the powder and the strip.

The use of a spray gun is not completely satisfactory because it is not capable, for obvious reasons, of providing a uniform coating of powder on the strip, more particularly when used in a large commercial installation where the strip is travelling at high speeds and is of a Width which is in excess of say 18 inches.

The use per se of the step of electrostatically charging the particles has of course met with a certain amount of success but, when used in combination with a spray gun, it does not affect the dispersion of the particles to the extent of providing a uniform coating.

It is among the objects of the present invention to provide an improved apparatus for coating, with metalli: powder, continuously moving metal strip, with particular reference to strip having a width in excess of 18 inches, which apparatus and its method of operation produces improved dispersion of the particles and thus a coating of uniform depth.

According to the present invention, there is provided an apparatus operable to perform a method of coating continuously moving metal strip with powder by feeding the powder through a metering device in such manner as to produce a plurality of uniformly spaced streams of powder across the width of the material to be coated, passing the streams of powder so formed through a diffusion device to produce a diffused cloud of particles which falls onto the moving strip in a uniform manner, and simultaneously imparting to the particles of the powder an electrostatic charge.

According to the invention furthermore, there is provided apparatus for coating continuously moving metal strip with powder which comprises a hopper for the powder, a metering device for receiving powder from the hopper, which device is arranged to produce a plurality of uniformly spaced streams of powder across the width 3,426,730 Patented Feb. 11, 1969 of the material to be coated, a diffusion device arranged to receive the streams of powder and to convert them into a diffused cloud of particles, and electric power means associated with the diffusion device for imparting to the particles of the powder an electrostatic charge.

Preferably the metering device comprises a drum formed with a plurality of spaced peripheral grooves for receiving the powder in predetermined quantities.

Preferably also the diffusion device comprises a vibratory screen consisting of one or more horizontally disposed layers of wire mesh, the screen being charged by a source of high voltage electric current whereby the --particles of the powder receive an electrostatic charge during their passage through the vibratory screen.

The invention is illustrated by way of example in the accompanyin g drawings in which,

FIGURE 1 is a schematic layout of one form of apparatus according to the invention, and

FIGURE 2 is a view in the direction of the arrow 2 of FIGURE 1.

Referring to the drawings, the apparatus comprises generally a hopper 3 for the powder, a metering roll 4 arranged immediately below the hopper 3 to receive and dispense predetermined quantities of powder therefrom, and a vibratory screen 5 arranged below, and in spaced relation with, the metering roll 4, all of which are supported on a frame, generally indicated at 6, so that they are disposed above a strip S to be treated, the strip S being supported on rolls 7 and moved continuously in the direction of the arrow 8.

The metering roll 4 is supported for rotation about its axis 9 and, for this purpose, is driven by a variable speed motor 10 via a belt or chain 11, or via gearing. The roll 4 is formed with spaced circumferential grooves 12, which are preferably of rectangular cross-section, the grooves 12 being arranged to receive powder stored in the hopper 3. v

The hopper 3 consists of a container having side walls 13 and end walls 14, the side walls 13 resting on the surface of the roll 4, via roller hearings or the like 15, and the end walls 14 being held in tight engagement with the roll 4 to provide a seal to prevent the escape of powder longitudinally along the roll 4.

The sides proper of the hopper 3 consists of a retaining blade 16, which extends lengthwise of the hopper, and bears, at one end, on the roll 4, and a compacting blade 17 which is supported, on one end of a secondary wall 18, so that it extends tangentially with respect to the surface of the roll 4. The purpose of the compacting blade 17 is to force the powder into the grooves 12 as the roll 4 rotates in the direction indicated by the arrow.

The blades 16 and 17 are of spring steel and the blade 17 preferably extends slightly beyond the point of contact with the roll to provide an entry opening for the powder which is dragged under the blade by the movement of the roll 4.

A vibrating plate 19 operated by a vibrator device 20 extends into the hopper 3 to efflfect agitation of the powder.

As indicated above, powder is pressed into the grooves 12 by the compacting blade 17 and it will be obvious that, at the same time, a certain amount of powder will also adhere to the lands between the grooves 12. In order to ensure accurate metering of the powder, this surplus powder is removed by a scraper blade 21, of spring steel, and falls into a container 22.

The compacted and accurately metered powder, the volume of which can be varied by varying the speed of rotation of the roller 4, is removed from the grooves 12 by means of finger elements 23 which extend into the grooves at a position diametrically opposite the hopper 3.

Thus, it will be seen that the powder which is chiefly in the form of powder particle agglomerates containing large numbers ofparticles loosely bound together by virtue of being compressed in the grooves 12, leaves the metering roll 4 in the form of a plurality of spaced streams.

The streams of powder so formed then fall into the vibratory screen 5 as indicated in FIGURE 1. The screen 5 consists of a frame 24 within which is supported one or more mesh screens 25, the frame being suspended via resilient means 26 on insulator blocks 27 secured to the main framework 6. In order to effect vibration of the screen 5 in a horizontal planeat right angles to the axis of rotation of the roll 4, a vibratory mechanism 28 is operatively associated with the frame 24.

A high voltage source 29 is connected, via line 30, to

the frame 24 and charges the screen to about 30 k v. po-- tential relative to the strip S which is earthed as indicated at 31.

As the streams of agglomerated particles of powder fall onto the vibratory screen from the roll 4 they are gradually dispersed into their constituent particles by. successive impact therewith. Particles leave the screen in a diffused cloud, which is uniform in density, in directions along and at rght angles to the axis of the metering roller. The'particles acquire an electrostatic charge by impact with the screen during their passage therethroughand are consequently attracted to the earthed strip to which they adhere strongly in a uniform layer.

The electrostatic field between the screen and the strip also exercise some dispersive effect on the particle cloud, tending to prevent reagglomeration of the particles.

It will be understood that the number of layers of mesh in the screen, the mesh size, andthe frequency and amplitude of the vibration appliedto-the screen can .be varied to provide good dispersion of grades of powder differing widely infineness and ease ofbreakdown. I

Good results have been achievedwith mesh openings in the ranged/ square to square when using aluminium powder in the particle size range of 120 mesh to dust.

What is claimed is: I

1. Apparatus for coating. ,continuously movingstrip metal with metallic powder which comprises ahopper for said powder, a metering device arranged in close con with said hoppento receive saidpowder, said metering device consisting of a roll formed with a plurality of spaced circumferential grooves .to receive a predetermined quantity of said powder, drive means for causing rotation of said roll, scraper means for removing said powder from said grooves and to produce a plurality of streams of said powder across the width of said strip to be coated, a diffusion device consisting of a -frame, at least one mesh screen supported in said'frame, and resilient means for suspending said frame from fixed supports, a vibratory mechanism operatively associated with said frame to cause reciprocation of'said screen in a horizontal plane, and electric power meansassociated with said screen for imparting to the particles of said powder an electrostatic charge. Q

4. Apparatus forcoating continuously moving strip metal with metallic powder which comprises a hopper for said powder, a meteringdevice' arranged in close contact with said hopper toreceive said'powder, said metering device consisting of a roll formed with a plurality of' compacting-said powder in said grooves, scraper means 1 in said frame, and resilient means for suspending said tact" with said hopper to receive said powder, said meter- 7 ing device consisting of a roll formed with a plurality of spaced circumferential grooves to receive a predetermined 7 quantity of said powder, drivemeans' for causing rota tion of said'roll, scraper means for',removing saidpowI-.

der from said grooves and to" prodtice' plurality of streams of said powder across the .width of said strip to be coated, a diffusion device arranged to receive said streams of powder and to convert them: into a diffus ed cloud of particles, and electric power, means for impart-j ing to said particles an electrostatic charge.

2. Apparatus for coating continuously moving. strip meta l with metallic powder which comprises a'.hopper determined quantity of said powder, drive means ,for

causing rotation of said roll, scraper means for removing s'aidpowder from said grooves and to produce a plurality' 'of streams of said powder across the width of said strip'to be coated, a diffusion device consisting of a frame, at least .one mesh screen supported in said frame, and resilient means for suspending said frame from fixed supports, and electric power means associated with said screen for imparting to the particles of said powder an electrostatic charge.

3. Apparatus for coating continuously moving strip metal with metallic powder which comprises a hopper for said powder, a metering device arranged in close contact from from fixed supports, and electric power means associated with said screen for imparting to the particles of said powder an electrostatic charge.

5. Apparatus for coating continuously moving strip metal with metallic powder which comprises a hopper for saidpowder, a' metering device'arranged in close contact with said hopper to receive said powder, said metering device'consistirig of a roll formed with a plurality of spaced circumferential grooves toreceive a predeterminedquantity of said powder, drive means for causing'rotationof said roll, means for compacting said powder in said grooves, scraper means for removing surplus powder from the surface of said roll, scraper means for removing said powder from said grooves and to produce a plurality of streams of said powderacross the width p of said strip to be coated, a diffusion device consisting of a frame, at least one mesh screen supported in said frame, 'and fesilient' means for suspending said frame from fixed supports, a vibratory mechanism operatively associated with said frame to cause reciprocation of said screen in 'ahorizontal plane, and electric power means associated with said screen for imparting to the particles of said powder an electrostatic charge.

References Cited UNITED STATES PATENTS Grossteinbeck et al. 118-636 X WILLIAM D. MARTIN, Primary Examiner. EDWARD J. CABIC, Assistant Examiner.

U.S. Cl. X.R. 

